Yes, there was every reason to believe that fighting a defensive war that eventually an armistice would be reached. The level of death tolerable to the Illinois Butcher ™, done in the name of the tyranny, is what was under estimated. By todays standards what was done then was a war where 4-5 million died(adjusted for population growth) Do you think we would have accepted that casualty rate in WWII? I doubt it. Let say the liberation of Africa in 1942 had cost a million GI's. How would it have turned out differently? I say things then would have been different. The only belligerent that would tolerate those casualty rates was the USSR. Even Japan gave up.
Death toll as % of population WBTS: 2%.
Death tolls in WWII by country:
USA .32%
Poland 17%
USSR 14%
UK .94%
Germany 8 to 11%
Japan 4 to 5%
Italy 1%
http://en.wikipedia.org/wiki/World_War_II_casualties#Total_deaths
Comparing numbers is complicated by numerous factors, such as which deaths should be classified as war deaths, which part of genocidal campaigns, etc.
What springs to the eye for anyone who knows anything about history is how low these percentages are compared to wars in earlier centuries.
Mongol conquest of Central Asia, Iran and Iraq: 50% to 90%.
Most of the “changes of dynasty” in Chinese history reduced the population by 1/4 to 2/3.
30 Years War killed 1/3 to 1/2 population of Germany.
English Civil War killed 10% of England, 20% of Scotland, 30% of Ireland.
Japan did not give up in WWII because the casualty rates were unacceptable.
They gave up because they had lost the ability to fight back effectively and (more importantly) because the moral shock of the A bomb finally gave those who wanted to give in the upper hand over the fight till everybody is dead crowd. And even then the extremists almost prevented the surrender.
Oh, I forgot the deadliest war of modern times.
http://en.wikipedia.org/wiki/Paraguayan_War
60% to 90% of population dead. Took place during and after our War. Paraguay picked a fight with an alliance of Uruguay, Argentina and Brazil. Quick look at map indicates this not a good idea.